Jun. 29, 2013

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Written by

Jake Van Camp

A doe takes care of newborn twin fawns in June in Ephraim. Research shows it's uncommon for both twins to survive until September, when the average fawn ratio in each deer herd unit comes close to one fawn per adult doe. / Gannett Wisconsin Media

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When a deer hunter comes home empty-handed from the nine-day gun-deer season, most of the blame for his or her failures gets pointed directly at the Wisconsin Department of Natural Resources for not supplying enough deer in the hunter’s beloved unit.

The DNR promises however, it has a method to the deer population madness.

Jeff Pritzl, wildlife supervisor in the DNR’s Northeast District, understands that every hunter wants to harvest a deer each season, but that is not the main goal the DNR is trying to accomplish. Its goal is to try and ensure that each year the population is strong enough to sustain itself so hunters get an opportunity to harvest deer each year.

The DNR has more obligations than maintaining the deer herd in units across the state, but that might be the most analyzed and scrutinized aspect.

A number of things go into what the DNR uses to determine deer population and potential each year. The Winter Severity Index is a measuring tool to determine how harsh a winter the deer have had. There are three-dozen citing locations across the north where the DNR analyzes snow depth and weather measurements to determine whether the winter was mild, moderate or severe based on a 1-to-100 scale. The number then gives them an indication of the productivity potential for that unit’s herd for the following year.

It’s important to note that every unit has its own individual growth rate average. Just because one unit might have a growth rate of 40 percent does not mean the unit next to it is going to be the same. Productivity rate simply means how much the herd grows from January to September, meaning fawn survival rate. If a unit has a 40 percent survival rate, then for every 100 deer in January in an area, 140 deer would be in that area in September. Each unit has its own number, and they use the average to determine how difficult the winter had been. Once they have it, they can begin to determine the number of potential doe permits to hand out.

The number of doe permits is also different in each area, but for a couple different reasons. Every unit has a quota success rate and a goal population. Goal population is determined by the previous year’s harvest, which is the mechanism for the Sex-Age-Kill formula.

The Sex-Age-Kill is short for the sex of each deer harvested, age of the deer when harvested, and the total harvested. This formula works because Wisconsin hunters have to register the deer they kill, which gives the DNR and the wildlife management team a more accurate perception of the population for each unit.

For example, Unit 50 has an average kill rate of roughly 30 to 35 percent for the doe permits the unit sells. The DNR knows this from the years of data it has collected from past gun-deer seasons, and sets a harvest goal based on the success rate of hunters in each unit, and the doe permit numbers hinge off that percentage.

Last season, of the 4,500 permits issued in Unit 50, 990 were filled, a 22 percent kill rate. That number is off the mark from typical years, but still is OK in the DNR’s view because it’s only one harvest year. This season, Unit 50 has a harvest goal of 500, putting 1,575 permits for sale. Pritzl understands that when the initial permit numbers come out, they can be a shock to a hunter’s system, but the reality is the DNR has a pretty good idea from the research on each unit how many of that number are going to be harvested, and that number should be a hunter’s focus instead.

“Every unit has its own personality when it comes to permits,” Pritzl said. “We often have arguments with people in March about the overall number, but as long as the success rate holds true, the large number won’t be quite as a concern then.”

Fawn survival also depends on what type of area the deer is born into. On average, there is a 60 percent survival rate in the agricultural areas and a 30 percent survival rate in forested land. Predation is a factor, but indirectly. The main cause is because the northern forest is not as fruitful in its production as agricultural land, despite the fact there is more forest land.

The 60 percent survival rate in areas such as Kewaunee or Manitowoc counties occur because the habitat is more plentiful, keeping the adult doe healthier and thus able to care for her young and protect and raise them during the early-development process.

Areas such as Florence and Forest counties typically have a 30 percent fawn survival rate because the adult doe may not be able to get the nutrients she needs. The adult doe may abandon her young simply because she cannot give it the care it needs because she is not healthy enough, thus allowing predation to occur. The better the body condition for the adult doe, the higher success rate for her young, making agricultural land much more successful for fawns to survive.

However, Pritzl said that by September, research shows the average fawn ratio in each unit comes close to one fawn per adult doe.

“Generally, you are averaging one fawn to one doe, and that kind of covers the averages to the twins that survive to the does that lose a fawn or lose both fawns and have none when they get into September,” Pritzl said. “Twins are the most common number of fawns born, but getting both of them to September isn’t very common, so it typically averages out by the time bow-hunting comes around.”

All of this information is used and analyzed by the DNR to make the best decision in each unit regarding the health and future stability of white-tailed deer, all while trying to maintain quality customer satisfaction.

It’s not a flawless system, but the DNR will continue to work hard each year so we have quality wildlife management for years to come.